168 THE BIOLOGY OF THE SEASONS 



child a tradition operative in various ways through 

 memory of what has been seen, through models to imitate, 

 and through permanent registration in books. Similarly, 

 there may be a distantly analogous tradition among wrens 

 and weaver-birds, thrushes and chaffinches, as to the fit and 

 proper nest to build. In support of this view, it is said, for 

 instance, that chaffinches transported to New Zealand no 

 longer build the typical chaffinch nest. They have got 

 beyond the tradition. 



Against Wallace's theory is the obvious fact that the 

 young birds do not see the building of the nest in which they 

 are hatched, but he supposes it to be sufficient that the young 

 birds before they leave the nest have " ample opportunities 

 of observing its form, its size, its position, the materials 

 of which it is constructed, and the manner in which those 

 materials are arranged." It may also be that the young 

 birds follow the lead of their seniors in nest-building the 

 following year, learning as they go along, and in some cases 

 they may not be ready for nest-building the first Spring, and 

 thus have further opportunities for watching what the older 

 birds do. But the fact is that careful experiments are 

 necessary before we can decide between the view that nest- 

 building is in the main an instinctive activity and Wallace's 

 conclusion that he cannot find in nest-building " a particle 

 of evidence to show the existence of anything beyond those 

 lower reasoning and imitative powers which animals are 

 universally admitted to possess." 



Mr. Pycraft, on the other hand, writes : " In spite of the 

 dogmatic assertions of this eminent naturalist, there is 

 absolutely not only no evidence in support of his contention 

 that birds build by imitation, but all the known facts are 

 directly against him." . . . Thus " wild birds taken from 

 the nest before they can see, and kept in captivity under 

 suitable conditions, will, at the appropriate time, build a 



